 	     att (attributes ctx)
 	     uda (up-down-arrows ctx)]
 	 (and (forall [g obj]
-		(exists [ [h _] uda ]
+		(exists [[h _] uda]
 		  (= g h)))
 	      (forall [m att]
-		(exists [ [_ n] uda ]
+		(exists [[_ n] uda]
 		  (= m n)))))))
 
 (defn context-object-closure

  (for [objs (context-extents ctx)]
    [objs, (object-derivation ctx objs)]))

;; Common Operations with Contexts

(defn dual-context
  "Dualizes context ctx, that is $(G,M,I)$ gets $(M,G,I^{-1})$."

			(set-of [[g_2 2] [m_1 1]]
				[g_2 (objects ctx-2)
				 m_1 (attributes ctx-1)]))]
    (make-context-nc new-objs new-atts new-inz)))

(defn context-product
  "Computes the context product of ctx-1 and ctx-2, that is
